This invention relates to an automatic load leveling pump for use in combination with conventional air adjustable shock absorbers or air bags.
Currently, automotive vehicles are available with either air or hydraulic automatic load leveling systems. An automatic system, such as is disclosed in U.S. Pat. No. 4,017,099 uses conventional air shocks with an electrically powered air compressor to extend the shocks and an electronic height sensing mechanism to control the amount of air pumped into the shocks by the compressor. Such systems are complex, costly, and they constitute a power drain on the vehicle electrical system. Hydraulic load leveling systems, such as are disclosed in U.S. Pat. Nos. 3,653,676, and 3,649,044, use engine-driven or electric motor-driven hydraulic pumps to pump hydraulic fluid into the rear shocks. Because of the incompressibility of the hydraulic fluid, a separate gas accumulator or a gas-filled shock is necessary to soften the ride characteristic. A mechanical height-sensing mechanism controls the amount of fluid pumped into the shocks. Also available are self-pumping load leveling shock absorbers whose pumping action is powered by the relative motion of the vehicle frame and axle. Such self-pumping shocks are complex and costly and suffer from reduced pumping efficiency as the shock absorber is extended.
The present invention provides an automatic load leveling air pump for use with an air adjustable shock absorber. The pump includes a housing connected to a vehicle axle and a pump piston connected to the vehicle frame. A feedback device slides in the housing in response to air pressure and defines a compression chamber in cooperation with the pump piston and the housing. The feedback device includes a pair of clutch portions which move together to radially expand one of the portions into frictional engagement with the housing upon compression of the pump. The feedback device moves in the housing in response to increasing shock absorber pressure to maintain a substantially constant compression ratio for the pump as the separation between the frame and axle increases. A mechanical height sensing valve cooperates with the pump to maintain a substantially constant separation between the frame and axle despite changes in vehicle loading.